1. Field of the Invention
This invention relates to bottle inspection systems and more particularly to bottle inspection systems using pressurized air in a timed cycle to detect leaks and dents in blow molded plastic bottles.
2. Description of the Prior Art
Blow molded plastic bottles have gained popularity and have greatly replaced glass bottles or other containers. Blow molded plastic bottles are relatively inexpensive and are unbreakable.
In recent years, the cost of plastics has greatly increased. On the other hand, the thickness of the plastic wall of the blow molded plastic bottles are greatly decreased to compensate for the increase in price. One of the incident problems resulting from the decrease in the thickness of the walls has been the increase incidence of pinholes and other defects such as dents or uncut flanges. The use of a defective bottle that has a pinhole is a loss in not only the bottle but also contents that have been placed within the bottle. The loss of the contents within the bottle is often many times the original cost of the bottle.
A bottle having a dent is also defective in that a certain sized bottle will not contain the predetermined amount of liquid or other contents if it has such a dent. The shortage of the material within the container can have bad side effects such as angry consumers and returned goods.
A bottle having a defective aperture is also defective. Plastic caps seal the blow molded bottles. The plastic cap has a wedge or ridge that abuts the inner edge of the bottle aperture. To promote a tight seal between the cap ridge and aperture, the aperture has an inwardly extending flange which is depressed by the ridge of the cap. If the aperture is not round or has a notch within its flange, the plastic cap will not adequately seal the aperture.
A bottle having an uncut flange can jam a conveyor line and cause a loss worth much more than the bottle itself. A flange can tip the bottle so it can get caught by a post or other obstacle adjacent the conveyor. Other bottles proceeding along the conveyor will be blocked by the caught bottle and can tip off of the conveyor or can back up causing a temporary shut down in operation while the bottles are straightened out. The bottle having an uncut flange can also get caught within a filling station and cause the loss of contents to be filled within that bottle.
A bottle inspection system is needed to detect both leaks and dents and other imperfections in the blow molded plastic bottles. An apparatus is needed to detect dents and leaks without permanently distorting the bottle by use of any excess testing pressure within the bottle container.
Previous testing apparatus have used either air pressure or a predetermined volume of air to detect leaks within the walls of the bottle. One such apparatus is disclosed is U.S. Pat. No. 3,495,441 issued to Laub on Feb. 17, 1970. The Laub patent discloses a leak detector that uses air pressure to determine a leak within plastic containers. The apparatus has a plurality of extendible shafts that ride upon a cam to follow a circular conveyor. The shafts have a spout which can extend into an aperture of the bottle. The bottle aperture is sealed against two sealing washers. Air is pumped into the bottle through the spout until a pressure switch is opened which cuts off the air to the bottle. If the bottle loses pressure while sealed, the pressure switch is reclosed and an ejection mechanism is activated. The ejection mechanism consists of a holding relay which activates a solenoid. The solenoid controls an air ejection nozzle so that if a defective bottle is tested, the ejection nozzle blows the bottle off the conveyor.
Another leak detector is disclosed in U.S. Pat. No. 3,805,593 issued to Sandoz et al on Apr. 23, 1974. The Sandoz patent discloses an apparatus that is completely self-contained and does not require an outside pressure source. A spout is introduced into a bottle and sealed therein. The spout is operably attached to a piston and cylinder. The bottle is lifted up with elevation of an apparatus platform which also lifts the cylinder. The piston is stationary and forces air from the cylinder into the bottle. Air pressure is created therein and is detected by a pressure sensitive switch.
With the advent of thinner plastic bottles, an apparatus is needed to detect dents within the bottle and uncut flanges as well as leaks.